Processing of acid containing hydrocarbons

ABSTRACT

A method for thermally cracking an organic acid containing hydrocarbonaceous feed wherein the feed is first processed in a vaporization step operated under conditions designed to vaporize and transmit a significant amount of the acid species in the feed to a thermal cracking furnace.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the thermal cracking of acid containinghydrocarbon feedstocks using a vaporization unit in combination with atleast one thermal cracking furnace. More particularly, this inventionrelates to using a vaporization unit to drive a significant amount ofacid species from a feedstock into at least one thermal crackingfurnace.

2. Description of the Prior Art

Thermal cracking (pyrolysis) of hydrocarbons is a petrochemical processthat is widely used to produce olefins such as ethylene, propylene,butenes, butadiene, and aromatics such as benzene, toluene, and xylenes.

Basically, a hydrocarbon containing feedstock is mixed with steam whichserves as a diluent to keep the hydrocarbon molecules separated. Thesteam/hydrocarbon mixture is preheated in the convection zone of thefurnace to from about 900 to about 1,000 degrees Fahrenheit (F), andthen enters the reaction (radiant) zone where it is very quickly heatedto a severe hydrocarbon thermal cracking temperature in the range offrom about 1,400 to about 1,550 F. Thermal cracking is accomplishedwithout the aid of any catalyst.

This process is carried out in a pyrolysis furnace (steam cracker) atpressures in the reaction zone ranging from about 10 to about 30 psig.Pyrolysis furnaces have internally thereof a convection section (zone)and a separate radiant section (zone). Preheating functions areprimarily accomplished in the convection section, while severe crackingmostly occurs in the radiant section.

After thermal cracking, depending on the nature of the primary feed tothe pyrolysis furnace, the effluent from that furnace can containgaseous hydrocarbons of great variety, e.g., from one to thirty-fivecarbon atoms per molecule. These gaseous hydrocarbons can be saturated,monounsaturated, and polyunsaturated, and can be aliphatic, alicyclics,and/or aromatic. The cracked gas can also contain significant amounts ofmolecular hydrogen (hydrogen).

The cracked product is then further processed in the olefin productionplant to produce, as products of the plant, various separate individualstreams of high purity such as hydrogen, ethylene, propylene, mixedhydrocarbons having four carbon atoms per molecule, fuel oil, andpyrolysis gasoline. Each separate individual stream aforesaid is avaluable commercial product in its own right. Thus, an olefin productionplant currently takes a part (fraction) of a whole crude stream orcondensate, and generates there from a plurality of separate, valuableproducts.

Thermal cracking came into use in 1913, and was first applied to gaseousethane as the primary feed to the cracking furnace for the purpose ofmaking ethylene. Since that time the industry has evolved to usingheavier and more complex hydrocarbonaceous gaseous and/or liquid feedsas the primary feed for the cracking furnace. Such feeds can now employa fraction of whole crude or condensate which is essentially totallyvaporized while thermally cracking same. The cracked product cancontain, for example, about 1 weight percent (wt. %) hydrogen, about 10wt. % methane, about 25 wt. % ethylene, and about 17 wt. % propylene,all wt. % being based on the total weight of that product, with theremainder consisting mostly of other hydrocarbon molecules having from 4to 35 carbon atoms per molecule.

Natural gas and whole crude oil(s) were formed naturally in a number ofsubterranean geologic formations (formations) of widely varyingporosities. Many of these formations were capped by impervious layers ofrock. Natural gas and whole crude oil (crude oil) also accumulated invarious stratigraphic traps below the earth's surface. Vast amounts ofboth natural gas and/or crude oil were thus collected to formhydrocarbon bearing formations at varying depths below the earth'ssurface. Much of this natural gas was in close physical contact withcrude oil, and, therefore, absorbed a number of lighter molecules fromthe crude oil.

When a well bore is drilled into the earth and pierces one or more ofsuch hydrocarbon bearing formations, natural gas and/or crude oil can berecovered through that well bore to the earth's surface.

The terms “whole crude oil” and “crude oil” as used herein means liquid(at normally prevailing conditions of temperature and pressure at theearth's surface) crude oil as it issues from a wellhead separate fromany natural gas that may be present, and excepting any treatment suchcrude oil may receive to render it acceptable for transport to a crudeoil refinery and/or conventional distillation in such a refinery. Thistreatment would include such steps as desalting. Thus, it is crude oilthat is suitable for distillation or other fractionation in a refinery,but which has not undergone any such distillation or fractionation. Itcould include, but does not necessarily always include, non-boilingentities such as asphaltenes or tar. As such, it is difficult if notimpossible to provide a boiling range for whole crude oil. Accordingly,whole crude oil could be one or more crude oils straight from an oilfield pipeline and/or conventional crude oil storage facility, asavailability dictates, without any prior fractionation thereof.

Natural gas, like crude oil, can vary widely in its composition asproduced to the earth's surface, but generally contains a significantamount, most often a major amount, i.e., greater than about 50 weightpercent (wt. %), methane. Natural gas often also carries minor amounts(less than about 50 wt. %), often less than about 20 wt. %, of one ormore of ethane, propane, butane, nitrogen, carbon dioxide, hydrogensulfide, and the like. Many, but not all, natural gas streams asproduced from the earth can contain minor amounts (less than about 50wt. %), often less than about 20 wt. %, of hydrocarbons having from 5 to12, inclusive, carbon atoms per molecule (C5 to C12) that are notnormally gaseous at generally prevailing ambient atmospheric conditionsof temperature and pressure at the earth's surface, and that cancondense out of the natural gas once it is produced to the earth'ssurface. All wt. % are based on the total weight of the natural gasstream in question.

When various natural gas streams are produced to the earth's surface, ahydrocarbon composition often naturally condenses out of the thusproduced natural gas stream under the then prevailing conditions oftemperature and pressure at the earth's surface where that stream iscollected. There is thus produced a normally liquid hydrocarbonaceouscondensate separate from the normally gaseous natural gas under the sameprevailing conditions. The normally gaseous natural gas can containmethane, ethane, propane, and butane. The normally liquid hydrocarbonfraction that condenses from the produced natural gas stream isgenerally referred to as “condensate,” and generally contains moleculesheavier than butane (C5 to about C20 or slightly higher). Afterseparation from the produced natural gas, this liquid condensatefraction is processed separately from the remaining gaseous fractionthat is normally referred to as natural gas.

Thus, condensate recovered from a natural gas stream as first producedto the earth's surface is not the exact same material, composition wise,as natural gas (primarily methane). Neither is it the same material,composition wise, as crude oil. Condensate occupies a niche betweennormally gaseous natural gas and normally liquid whole crude oil.Condensate contains hydrocarbons heavier than normally gaseous naturalgas, and a range of hydrocarbons that are at the lightest end of wholecrude oil.

Condensate, unlike crude oil, can be characterized by way of its boilingpoint range. Condensates normally boil in the range of from about 100 toabout 650 F. With this boiling range, condensates contain a wide varietyof hydrocarbonaceous materials. These materials can include compoundsthat make up fractions that are commonly referred to as naphtha,kerosene, diesel fuel(s), and gas oil (fuel oil, furnace oil, heatingoil, and the like).

Atmospheric residuum (“resid,” “residua”) obtained from a conventionalatmospheric thermal distillation tower can have a wide boiling range,particularly when mixtures of residua are employed, but will generallybe in a boiling range of from about 600 F to the boiling end point whereonly non-boiling entities remain. These resids are primarily composed ofa gas oil component boiling in the range of from about 600 to about1,000 F and a heavier fraction boiling in a temperature range of fromabout 1,000 F up to its end boiling point where only non-boilingentities remain.

In contrast to an atmospheric tower, a vacuum assisted thermaldistillation tower (vacuum tower) typically separates this gas oilcomponent from its associated heavier fraction aforesaid, thus freeingthe gas oil fraction for separate recovery and use elsewhere.

The olefin production industry is now progressing beyond the use offractions of crude oil or condensate (gaseous and/or liquid) as theprimary feed for a cracking furnace to the use of whole crude oil, crudeoil residuum, and/or condensate itself as a significant part of thatfeed.

U.S. Pat. No. 6,743,961 (hereafter “USP '961”) recently issued to DonaldH. Powers. This patent relates to cracking whole crude oil by employinga vaporization/mild cracking zone that contains packing. This zone isoperated in a manner such that the liquid phase of the whole crude thathas not already been vaporized is held in that zone untilcracking/vaporization of the more tenacious hydrocarbon liquidcomponents is maximized. This allows only a minimum of solid residueformation which residue remains behind as a deposit on the packing. Thisresidue is later burned off the packing by conventional steam airdecoking, ideally during the normal furnace decoking cycle, see column7, lines 50-58 of that patent. Thus, the second zone 9 of that patentserves as a trap for components, including hydrocarbonaceous materials,of the crude oil feed that cannot be cracked or vaporized under theconditions employed in the process, see column 8, lines 60-64 of thatpatent.

U.S. Pat. No. 7,019,187, issued to Donald H. Powers, is directed to theprocess disclosed in USP '961, but employs a mildly acidic crackingcatalyst to drive the overall function of the vaporization/mild crackingunit more toward the mild cracking end of the vaporization (withoutprior mild cracking)—mild cracking (followed by vaporization) spectrum.

U.S. Pat. No. 7,404,889, issued to Donald H. Powers, is directed to theprocess disclosed in USP '961, but uses atmospheric residuum as thedominant liquid hydrocarbonaceous feed for the vaporization unit andfurnace.

The disclosures of the foregoing patents, in their entirety, areincorporated herein by reference.

U.S. patent application Ser. No. 11/365,212, filed Mar. 1, 2006, havingcommon inventorship and assignee with USP '961, is directed to the useof condensate as the dominant liquid hydrocarbonaceous feed for thevaporization unit and furnace.

U.S. Application Publication 2007/0066860 John S. Buchanan et al.,published Mar. 22, 2007, discloses the thermal cracking of crudes thathave a high Total Acid Number (TAN) using a flash drum unit incombination with a thermal cracking furnace. This Publication disclosesthat its flash drum effects only a physical separation of the two phases(vapor and liquid) entering that drum. That is to say, the compositionof the vapor phase leaving the flash drum is disclosed to besubstantially the same as the composition of the vapor phase enteringthat drum. Likewise, the composition of the liquid phase leaving thesame flash drum is disclosed to be substantially the same as thecomposition of the liquid phase entering that drum. Preferred high TANfeeds are disclosed to be crude or a feed stream that has previouslybeen subjected to a refinery process to remove resid. Thus, Buchanan etal. teach away from the use of resids in its process.

The Publication to Buchanan et al. further discloses that the naphthenicacids present in its high TAN feeds are substantially converted to CO,CO₂, and lower molecular weight acids such as formic, acetic, propionic,and butyric acids.

Organic acids, including, but not limited to, carboxylic acids,naphthenic acids and phenolic acids, are present to a growing extent inhydrocarbonaceous feeds such as crude oil, and are becoming a problemfor crude oil refining processors. Naphthenic acids are often singledout for consideration because they are particularly corrosive.

Most refineries are unable to process crude oils with total acid numbers(TAN) greater than 1.0 due to the highly corrosive nature of the acids,particularly naphthenic acids, above 400 F. As more and more of theWorld's hydrocarbon production capacity is required to meet demand, theuse of these acid containing feed stocks, particularly crude oils, isrequired to meet worldwide demand growth.

By this invention, organic acid containing feedstocks such as wholecrude oil, and condensate, and organic acid containing fractions ofcrude oil, e.g., residua, are processed by a combination of avaporization unit and at least one thermal cracking furnace not only toreduce (convert or transform) the original acid content, but also toform additional thermal cracking feed from those feedstocks.

In addition, pursuant to this invention the aforesaid vaporization unitis deliberately operated to drive a substantial amount of acid speciesfrom the acid containing cracking feedstock into a thermal crackingfurnace. Many of the acid species driven to a cracking furnace by way ofthis invention would otherwise have been retained by the liquid bottomsproduct of the vaporization unit, and caused acid corrosion problemselsewhere in the plant where this bottoms product is subsequentlyprocessed.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided a unique processfor handling organic acid containing feedstocks that employs avaporization unit in combination with at least one thermal crackingfurnace wherein the vaporization unit is deliberately operated in amanner that removes from those feedstocks for transmission to thethermal cracking furnace a significant amount of acid species that wereoriginally present in those feedstocks and that would otherwise havebeen retained in the liquid bottoms product of the vaporization unit.

DESCRIPTION OF THE DRAWING

FIG. 1 shows one vaporization/cracking system useful in the process ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION

The terms “hydrocarbon,” “hydrocarbons,” and “hydrocarbonaceous” as usedherein do not mean materials strictly or only containing hydrogen atomsand carbon atoms. Such terms include materials that arehydrocarbonaceous in nature in that they primarily or essentially arecomposed of hydrogen and carbon atoms, but can contain other elementssuch as oxygen, sulfur, nitrogen, metals, inorganic salts, and the like,even in significant amounts. These terms include crude oil itself orfractions thereof such as gas oil, residuum, and the like. They alsoinclude natural gas condensate.

The term “gaseous” as used in this invention means one or more gases inan essentially vaporous state, for example, steam alone, a mixture ofsteam and hydrocarbon vapor, and the like.

Coke, as used herein, means a high molecular weight carbonaceous solid,and includes compounds formed from the condensation of polynucleararomatics.

An olefin producing plant useful with this invention would include apyrolysis (thermal cracking) furnace for initially receiving andthermally cracking the feed. Pyrolysis furnaces for steam cracking ofhydrocarbons heat by means of convection and radiation, and comprise aseries of preheating, circulation, and cracking tubes, usually bundlesof such tubes, for preheating, transporting, and cracking thehydrocarbon feed. The high cracking heat is supplied by burners disposedin the radiant section (sometimes called “radiation section”) of thefurnace. The waste gas from these burners is circulated through theconvection section of the furnace to provide the heat necessary forpreheating the incoming hydrocarbon feed. The convection and radiantsections of the furnace are joined at the “cross-over,” and the tubesreferred to hereinabove carry the hydrocarbon feed from the interior ofone section to the interior of the next.

In a typical furnace, the convection section can contain multiplesub-zones. For example, the feed can be initially preheated in a firstupper sub-zone, boiler feed water heated in a second sub-zone, mixedfeed and steam heated in a third sub-zone, steam superheated in a fourthsub-zone, and the final feed/steam mixture split into multiplesub-streams and preheated in a lower (bottom) or fifth sub-zone. Thenumber of sub-zones and their functions can vary considerably. Eachsub-zone can carry a plurality of conduits carrying furnace feed therethrough, many of which are sinusoidal in configuration. The convectionsection operates at much less severe operating conditions than theradiant section.

Cracking furnaces are designed for rapid heating in the radiant sectionstarting at the radiant tube (coil) inlet where reaction velocityconstants are low because of low temperature. Most of the heattransferred simply raises the hydrocarbons from the inlet temperature tothe reaction temperature. In the middle of the coil, the rate oftemperature rise is lower but the cracking rates are appreciable. At thecoil outlet, the rate of temperature rise increases somewhat but not asrapidly as at the inlet. The rate of disappearance of the reactant isthe product of its reaction velocity constant times its localizedconcentration. At the end of the coil, reactant concentration is low andadditional cracking can be obtained by increasing the process gastemperature.

Steam dilution of the feed hydrocarbon lowers the hydrocarbon partialpressure, enhances olefin formation, and reduces any tendency towardcoke formation in the radiant tubes.

Cracking furnaces typically have rectangular fireboxes with uprighttubes centrally located between radiant refractory walls. The tubes aresupported from their top.

Firing of the radiant section is accomplished with wall or floor mountedburners or a combination of both using gaseous or combinedgaseous/liquid fuels. Fireboxes are typically under slight negativepressure, most often with upward flow of flue gas. Flue gas flow intothe convection section is established by at least one of natural draftor induced draft fans.

Radiant coils are usually hung in a single plane down the center of thefire box. They can be nested in a single plane or placed parallel in astaggered, double-row tube arrangement. Heat transfer from the burnersto the radiant tubes occurs largely by radiation, hence the term“radiant section,” where the hydrocarbons are heated to from about 1,400F to about 1,550 F and thereby subjected to severe cracking, and cokeformation.

The initially empty radiant coil is, therefore, a fired tubular chemicalreactor. Hydrocarbon feed to the furnace is preheated to from about 900F to about 1,000 F in the convection section by convectional heatingfrom the flue gas from the radiant section, steam dilution of the feedin the convection section, or the like. After preheating, in aconventional commercial furnace, the feed is ready for entry into theradiant section.

The cracked gaseous hydrocarbons leaving the radiant section are rapidlyreduced in temperature to prevent destruction of the cracking pattern.Cooling of the cracked gases before further processing of samedownstream in the olefin production plant recovers a large amount ofenergy as high pressure steam for re-use in the furnace and/or olefinplant. This is often accomplished with the use of transfer-lineexchangers that are well known in the art.

With a liquid hydrocarbon feedstock downstream processing, although itcan vary from cracking plant to cracking plant, typically employs an oilquench of the furnace effluent after heat exchange of same in, forexample, the transfer-line exchanger aforesaid. Thereafter, the crackedhydrocarbon stream is subjected to primary fractionation to remove heavyliquids, followed by compression of uncondensed hydrocarbons, and acidgas and water removal there from. Various desired products are thenindividually separated, e.g., ethylene, propylene, a mixture ofhydrocarbons having four carbon atoms per molecule, fuel oil, pyrolysisgasoline, and a high purity hydrogen stream.

FIG. 1 shows a vaporization/cracking system that can operate on organicacid containing whole crude oil, condensate, fractions of whole crudeoil including residua, particularly atmospheric residua, and mixturesthere of as the dominant (primary) system feed.

FIG. 1 is very diagrammatic for sake of simplicity and brevity since, asdiscussed above, actual furnaces are complex structures.

Total Acid Number or TAN is a measure of the organic acid content of ahydrocarbonaceous material. Such organic acids include, but are notlimited to, at least one carboxylic acid species, at least onenaphthenic acid species, and/or at least one phenolic acid species.Other acid species such as the low molecular acids described hereinabove may also be present in less significant amounts.

TAN is determined by ASTM method D-644 and takes the units of milligrams(mg) KOH/kilogram (kg) of hydrocarbonaceous material being tested. Forsake of brevity, here in after the method of measurement and units arenot repeated.

Feed streams that contain organic acids as defined herein above and towhich this invention is applicable include any hydrocarbonaceousmaterial such as crude oil itself, one or more fractions of crude oilincluding residuum, particularly atmospheric resid, natural gascondensate, and mixtures of two or more thereof.

Carboxylic acid species are the most corrosive class of acids present inthe foregoing feed streams. Within the carboxylic acid class of acids,the naphthenic acid sub-group is the most corrosive and problematic inrespect of minimizing the corrosion of down-stream operating equipment.

The atmospheric resid feed employed in this invention can be from asingle or multiple sources, and, therefore, can be a single resid or amixture of two or more residua with or without other materials such ascrude oil and condensate. Atmospheric resid useful in this invention canhave a wide boiling range, particularly when mixtures of residua areemployed, but will generally be in a boiling range of from about 600 Fto the boiling end point where only non-boiling entities remain.

Atmospheric resid bottoms from an atmospheric thermal distillation towerare primarily composed of a gas oil component boiling in the range offrom about 600 to about 1,000 F and a heavier fraction boiling in atemperature range of from about 1,000 F up to its end boiling pointwhere only non-boiling entities remain.

A vacuum assisted thermal distillation tower (vacuum tower) typicallyseparates the gas oil component from its associated heavier fractionaforesaid, thus providing a different composition resid.

The amount of resid employed in feed 2 pursuant to this invention can bea significant component of the overall feed 2. The resid component canbe at least about 20 wt. % of the total weight of feed 2, but it is notnecessarily strictly within this range.

Depending on the specific physical and chemical characteristics of theresid added to feed 2, other materials can be added to that feed. Suchadditional materials can include light gasoline, naphtha, naturalgasoline and/or condensate. Naphtha can be employed in the form of fullrange naphtha, light naphtha, medium naphtha, heavy naphtha, or mixturesof two or more thereof. The light gasoline can have a boiling range offrom that of pentane (C5) to about 158 F. Full range naphtha, whichincludes light, medium, and heavy naphtha fractions, can have a boilingrange of from about 158 to about 350 F. The boiling ranges for thelight, medium, and heavy naphtha fractions can be, respectively, fromabout 158 to about 212 F, from about 212 to about 302 F, and from about302 to about 350 F.

The amount of light material(s) thus deliberately added to the resid infeed 2 can vary widely depending on the desires of the operator, but theresid in feed 2, if present, can remain a significant component of thefeed 2 that is in line 10 and feeds vaporization unit 11.

FIG. 1 shows a thermal liquid cracking furnace 1 wherein ahydrocarbonaceous primary feed 2 containing, for example, at least onecarboxylic acid species is passed into an upper feed preheat sub-zone 3in the upper, cooler reaches of the convection section of furnace 1.Steam 6 is also superheated in an upper level of the convection sectionof the furnace.

The pre-heated cracking feed stream is then passed by way of pipe (line)10 to a vaporization unit 11 (fully disclosed in USP '961), which unitis separated into an upper vapor vaporization zone 12 and a lowervaporization zone 13. This unit 11 achieves primarily (predominately)vaporization of at least a significant portion of the materials, e.g.,naphtha and gasoline boiling range and lighter fractions, that remain inthe liquid state after the pre-heating step 3.

Gaseous materials, both hydrocarbonaceous and acidic, that areassociated with the preheated feed as received by unit 11, andadditional gaseous materials, both hydrocarbonaceous and acidic, thatmay be formed under the particular conditions then prevailing in zone12, are removed from zone 12 by way of line 14. Thus, line 14 carriesaway essentially all the lighter hydrocarbon vapors, e.g., naphtha andgasoline boiling range and lighter, that are present in zone 12, and cancarry away some vaporous acid species. Liquid distillate present in zone12, with or without some liquid gasoline and/or naphtha, is removedthere from via line 15 and passed, along with still liquid acid species,into the upper interior of lower zone 13.

Zones 12 and 13, in this particular embodiment, are separated from fluidcommunication with one another by an impermeable wall 16, which can be asolid tray. Line 15 represents external fluid down flow communicationbetween zones 12 and 13. In lieu thereof, or in addition thereto, zones12 and 13 can have internal fluid communication there between bymodifying wall 16 to be at least in part liquid permeable by use of oneor more trays designed to allow liquid to pass down into the interior ofzone 13 and vapor up into the interior of zone 12. For example, insteadof an impermeable wall 16, a chimney tray could be used in which caseliquid within unit 11 would flow internally down into section 13 insteadof externally of unit 11 via line 15. In this internal down flow case,distributor 18 becomes optional.

By whatever way liquid is removed from zone 12 to zone 13, that liquidmoves downwardly into zone 13, and thus can encounter at least oneliquid distribution device 18. Device 18 evenly distributes liquidacross the transverse cross section of unit 11 so that the liquid willflow uniformly across the width of the tower into contact with packing19.

Steam 6 passes through superheat sub-zone 20, and then, via line 21 into a lower portion 22 of zone 13 below packing 19. In packing 19 liquidfrom stream 15 and steam from line 21 intimately mix with one anotherthus vaporizing some of liquid 15. This newly formed acidichydrocarbonaceous vapor, along with steam 21, is removed from zone 13via line 17 and can be added to the vapor in line 14 to form a combinedacidic hydrocarbon vapor product in line 25. Stream 25 can containessentially hydrocarbon vapor from feed 2, e.g., gasoline, naphtha,middle distillates, gas oils, a substantial amount of acidic speciesoriginally in feed 2, and steam.

Stream 17 thus represents a part of feed stream 2 plus steam 21 lesshydrocarbon liquid remainder from feed 2 that is present in bottomsstream 26. By operation of vaporization unit 11 pursuant to thisinvention, stream 25 contains a significant amount, if not most (e.g.,preponderance), of the organic acids that were present in the originalfeedstock 2, particularly the carboxylic and naphthenic acid species.

Stream 25 is passed through a header (not shown) whereby stream 25 issplit into multiple sub-streams and passed through multiple conduits(not shown) into convection section pre-heat sub-zone 27 of thermalcracking furnace 1. Section 27 is in a lower, and therefore hotter,section of furnace 1. Section 27 is used for preheating stream 25 to atemperature, aforesaid, suitable for thermal cracking in radiant zone29.

After substantial heating in section 27, stream 25, including organicacid species contained therein, passes by way of line 28 into radiantsection sub-zone 29. Again, the multiple, individual streams thatnormally pass from sub-zone 27 to and through sub-zone 29 are, for sakeof brevity, represented as a single flow stream 28.

In radiant firebox 29 of furnace 1, feed from line 28, which containsnumerous varying hydrocarbon components, including carboxylic acidspecies, is subjected to severe thermal cracking conditions asaforesaid. These thermal cracking conditions convert, or otherwisetransform, a significant amount, even preponderance (essentially all),of the carboxylic acids present into at least one of carbon monoxide(CO), carbon dioxide (CO₂), and lower molecular weight acids (formic,acetic, propionic, and butyric acids).

The cracked product leaves radiant firebox 29 by way of line 30 forfurther processing in the remainder of the olefin plant downstream offurnace 1 as described hereinabove and shown in detail in USP '961.

When using crude oil, condensate, resid, and the like, as thesignificant component(s) of feed 2, substantial amounts of distillates,some containing organic acids, are ultimately vaporized in unit 11,particularly zone 13, passed into furnace 1, and cracked therebyconverting such distillates into lighter components.

Feed 2 can enter furnace 1 at a temperature of from about ambient up toabout 300 F at a pressure from slightly above atmospheric up to about100 psig (hereafter “atmospheric to 100 psig”).

Feed 2 can enter zone 12 via line 10 at a temperature of from aboutambient to about 750 F, e.g., from about 500 to about 750 F, at apressure of from atmospheric to 100 psig.

Stream 14 can be essentially all hydrocarbon vapor formed from feed 2and is at a temperature of from about ambient to about 700 F at apressure from atmospheric to 100 psig. Stream 14 may or may not containsome of the acid species that were originally present in feed 2.

Stream 15 can be essentially all the remaining liquid from feed 2 lessthat which was vaporized in pre-heater 3 and zone 12, and is at atemperature of from about ambient to about 700 F at a pressure fromslightly above atmospheric up to about 100 psig (hereafter “atmosphericto 100 psig”).

Zone 12 can serve as a physical separation zone like that of the flashdrum in the publication of Buchanan et al. discussed here in above, and,in addition, can be operated at conditions that serve to causeadditional vaporization of liquid hydrocarbon and acid species that haveentered zone 12 by way of line 10.

Zone 13 is operated under conditions deliberately calculated not only tovaporize significant additional amounts of liquid hydrocarbons, but alsoto vaporize a significant, preferably preponderant (essentially all),amount of the organic acids, particularly carboxylic and naphthenic acidspecies, that were originally in feed 2 and remained in stream 15. Thisdrives a maximum amount of acid species into line 17 for transmission tofurnace 1.

Accordingly, pursuant to this invention vaporization unit 11, andparticularly zone 13 of that unit, is deliberately operated at atemperature in the range of from about 700 to about 1,100 F to form asubstantial amount of additional vaporous hydrocarbons and vaporousacids from the liquid it receives from zone 12 by way of line 15.

Thus, vaporization unit 11, operated pursuant to this invention, formssubstantial amounts of additional vaporous hydrocarbons andnon-disassociated (unaltered as to their chemical make-up) vaporousacids from the liquid present in the pre-heated feed stream 10.

Accordingly, the chemical composition, both hydrocarbonaceous andacidic, of the vapor phase leaving vaporization unit 11 by way of eachof lines 14, 17, and 25 is substantially different from the chemicalcomposition of the vapor phase entering unit 11 by way of line 10.Similarly, the chemical composition of the liquid phase leaving unit 11by way of line 26 is substantially different from the chemicalcomposition of the liquid phase entering unit 11 by way of line 10. Thatis to say unit 11 does more than just effect a physical separation ofthe two phases (liquid and vapor) that enters unit 11 by way of line 10.

The combination of streams 14 and 17, as represented by stream 25, canbe at a temperature of from about 600 to about 800 F at a pressure offrom atmospheric to 100 psig, and contain, for example, an overallsteam/hydrocarbon ratio of from about 0.1 to about 2.0, preferably fromabout 0.1 to about 1.0, pounds of steam per pound of hydrocarbon.

In vaporization zone 13, dilution ratios (hot gas/liquid droplets) willvary widely because the compositions of crude oil, fractions of crudeoil (particularly resid), and condensate vary widely. Generally, the hotgas, e.g., steam, hydrocarbon, and acid species at the top of zone 13and in line 17 can be present in a ratio of steam to hydrocarbon of fromabout 0.1/1 to about 5/1.

Steam is an example of a suitable hot gas introduced by way of line 21.Stream 6 can be that type of steam normally used in a conventionalcracking plant. Other materials can be present in the steam employed.All such gases are preferably at a temperature sufficient to volatilizea substantial fraction of the liquid hydrocarbon 15 that enters zone 13.Generally, the gas entering zone 13 from conduit 21 will be at leastabout 650 F, preferably from about 900 to about 1,100 F at fromatmospheric to 100 psig. Such gases will, for sake of simplicity,hereafter be referred to in terms of steam alone.

Stream 17 can, therefore, be a mixture of steam and hydrocarbon/acidspecies vapors that has a boiling point lower than about 1,100 F. Stream17 can be at a temperature of from about 600 to about 800 F at apressure of from atmospheric to 100 psig.

Steam from line 21 does not serve just as a diluent for partial pressurepurposes as is the normal case in a cracking operation. Rather, steamfrom line 21 provides not only a diluting function, but also additionalvaporizing and mild cracking energy for the hydrocarbons that remain inthe liquid state in unit 11. This is accomplished with just sufficientenergy to achieve 1) vaporization and/or mild cracking of heavierhydrocarbon components such as those found in whole crude oil and residand 2) vaporization of a significant amount, if not essentially all ofthe carboxylic acid species present. For example, by using steam in line21, substantial vaporization/mild cracking of feed 2 liquid hydrocarbonsis achieved. The very high steam dilution ratio and the highesttemperature steam are thereby provided where they are needed most asacidic liquid hydrocarbon droplets move progressively lower in zone 13.

Pursuant to this invention, hydrocarbons and acid species boilinglighter (lower) than about 1,100 F, all as defined hereinabove,remaining in the feed 10 of vaporization unit 11 of FIG. 1 will bevaporized in unit 11 and removed by way of either line 14 or 17 or bothand fed to furnace 1 as described hereinabove. In addition,hydrocarbonaceous entities heavier than the lighter entities mentionedabove in this paragraph can, at least in part, be mildly cracked orotherwise broken down in unit 11, particularly zone 13, to lighterhydrocarbonaceous entities such as those mentioned above, and those justnewly formed lighter entities removed by way of line 17 as additionalfeed for furnace 1. Acid species present will be vaporized in theiroriginal form, and removed by way of line 17 to furnace 1 fordisassociation or other chemical alteration in that furnace.

The liquid remainder of feed 10 is removed by way of line 26 fordisposition elsewhere. By way of the operation of vaporization unit 11,particularly zone 13, in the manner set forth above for this invention,a maximum (preponderant) amount, if not all, of the acid species,particularly carboxylic and naphthenic, originally present in feed 2will be vaporized and transmitted to furnace 1 for chemical destructiontherein. A preponderance of the highly corrosive naphthenic acid speciesoriginally present in feed 2 will, pursuant to this invention, be drivenby operation of vaporization unit 11 into furnace 1. In that furnace theacid species are at least one of destroyed in their entirety orconverted (transformed) into lower molecular weight, less corrosive acidspecies.

Since a significant amount, if not all, acid species originally in feed2 will, pursuant to this invention, be sent to furnace 1, bottomsproduct 26 of vaporization unit 11 will contain minimal, if any,carboxylic acid species that were originally found in feed 2. If acidspecies are present in product 26, they will generally be less corrosiveacids.

Accordingly, bottoms product 26 will, pursuant to this invention, beessentially non-corrosive in respect of its acid content, and can bemore easily and readily processed in other systems in the plant, e.g.,the quench oil and/or fuel oil systems, with little or no regard for anyacid corrosion tendency of stream 26, and sub-streams formed there from.

EXAMPLE

A Doba atmospheric residuum that has a TAN value of 4.5 is mixed inequal parts by weight with light gasoline and naphtha, resulting in ablend that has a TAN value of 2.25. This blend is fed into the preheatsection 3 of the convection section of pyrolysis furnace 1. This feedmixture 2 is at 260 F and 80 psig. In this convection section feed 2 ispreheated to about 690 F at about 60 psig, and then passes through line10 into vaporization unit 11 wherein a mixture of gasoline, naphtha andgas oil gases at about 690 F and 60 psig is separated in zone 12 of thatunit.

These separated gases are removed from zone 12 for transfer by way ofline 25 to the convection preheat sub-zone 27 of the same furnace.

The hydrocarbon liquid remaining from resid based feed 2, afterseparation from accompanying hydrocarbon gases aforesaid, is transferredto lower section 13 by way of line 15 and allowed to fall downwardly inthat section toward the bottom thereof.

Preheated steam 21 at about 1,050 F is introduced near the bottom ofvaporization zone 13 to give a steam to hydrocarbon ratio in section 13of about 1. The falling liquid droplets, both hydrocarbonaceous andacidic, are in counter current flow with the steam that is rising fromthe bottom of zone 13 toward the top thereof. With respect to the liquidfalling downwardly in zone 13, the steam to liquid hydrocarbon ratioincreases from the top to bottom of section 19.

A mixture of steam and hydrocarbon vapor 17 at about 750 F is withdrawnfrom near the top of zone 13 and mixes with the gases earlier removedfrom zone 12 via line 14 to form a composite steam/hydrocarbon vaporstream 25 containing about 0.5 pounds of steam per pound of hydrocarbonpresent. This composite stream is preheated in sub-zone 27 to about1,000 F at less than about 50 psig, and then passes into radiant fireboxsub-zone 29 for cracking at a temperature in the range of 1,400° F. to1,550° F. CO and CO₂ production is increased in the cracking furnacebecause of the conversion of carboxylic acids that are present in stream25.

Bottoms product 26 of unit 11 is removed at a temperature of about 900F, and pressure of about 60 psig, and passes to the downstreamprocessing equipment for further processing as desired.

Significant amounts of organic acids, including carboxylic acids, end upin stream 25, and are there after converted to CO, CO₂, and lowermolecular weight acids in the cracking furnace.

At the same time additional vaporous feed for that cracking furnace areformed by the vaporization of additional amounts of liquid feed by wayof the operation of vaporization unit 11, particularly vaporization zone13.

1. A method for thermally cracking in at least one thermal crackingfurnace a hydrocarbonaceous feedstock composed of at least onehydrocarbonaceous material, at least one of said hydrocarbonaceousmaterials containing at least one organic acid species, said methodcomprising preheating said feedstock to form a preheated streamcomprising an initial vaporous phase having an initial chemicalcomposition and an initial liquid phase having an initial chemicalcomposition, passing said preheated stream to a vaporization step inwhich a portion of said initial liquid phase is vaporized in a mannersuch that the chemical composition of the total of the vapor leavingsaid vaporization step is different from said initial chemicalcomposition of said initial vaporous phase and the chemical compositionof the remaining liquid leaving said vaporization step is different fromsaid initial chemical composition of said initial liquid phase, carryingout said vaporization step in a manner such that at least a significantamount of said at least one organic acid species is vaporized therein,and passing at least part of said vapor leaving said vaporization stepto said at least one thermal cracking furnace as at least part of thefeed therefore.
 2. The method of claim 1 wherein said hydrocarbonaceousfeedstock has a TAN of at least about 1.0 mg KOH/g feedstock.
 3. Themethod of claim 1 wherein said hydrocarbonaceous feedstock has a TAN ofat least about 0.5 mg KOH/g feedstock.
 4. The method of claim 1 whereinsaid hydrocarbonaceous feedstock is at least one of whole crude oil,condensate, residuum, and mixtures of two or more thereof.
 5. The methodof claim 1 wherein said hydrocarbonaceous feedstock is at least oneatmospheric residuum.
 6. The method of claim 1 wherein said at least oneorganic acid species includes at least one carboxylic acid species. 7.The method of claim 6 wherein said at least one carboxylic acid speciesincludes at least one naphthenic acid species.
 8. The method of claim 1wherein said vaporization step employs at least first and secondvaporization zones, said first vaporization zone receives said preheatedfeed stock comprising said initial vaporous phase and said initialliquid phase and at least separates said initial vaporous phase fromsaid initial liquid phase, said separated initial vaporous phasematerials are passed from said first vaporization zone to said at leastone thermal cracking furnace as feed therefore, said second vaporizationzone receives from said first vaporization zone preheated initial liquidphase materials that were not present as vapor in said firstvaporization zone and subjects such materials to at least one of heatingand mild cracking in said second vaporization zone until a significantamount of such materials in said second vaporization zone are vaporizedto form additional gaseous materials and leaving a liquid remainder, andsaid additional gaseous materials formed in said second vaporizationzone are removed there from and passed to said at least one thermalcracking furnace as feed therefore, whereby the chemical composition ofsaid additional gaseous materials formed in said second vaporizationzone is different from the chemical composition of said initial vaporousphase, and the chemical composition of said liquid remainder leavingsaid second vaporization zone is different from the chemical compositionof said initial liquid phase.
 9. The method of claim 8 wherein saidinitial liquid phase materials in said second vaporization zone aresubjected to a temperature in the range of from about 700 to about 1,100F.
 10. The method of claim 8 wherein initial liquid phase materials thatwere not present as vapor in said first vaporization zone are subjectedin said second vaporization zone to a temperature in the range of fromabout 700 to about 1,100 F, and an overall steam/hydrocarbon ratio offrom about 0.1/1 to about 5/1.
 11. The method of claim 8 wherein saidseparated initial vaporous phase materials from said first vaporizationzone contain at least some organic acid species, said removed additionalgaseous materials from said second vaporization zone contain asignificant amount of organic acid species, and said separated initialvaporous phase materials from said first vaporization zone and saidremoved additional gaseous materials from said second vaporization zoneare combined and the combined stream passed to said at least one thermalcracking furnace.
 12. The method of claim 11 wherein a preponderance ofsaid at least one organic acid species that were originally in saidhydrocarbonaceous feedstock is vaporized in said vaporization stepbefore passing to said at least one thermal cracking furnace.